| Nowadays,supercapacitors,also called electrochemical capacitors,have attracted great interest in energy storage because they fill the gaps between dielectric capacitors and batteries due to their higher energy density than dielectric capacitors and higher power density than batteries.Conductive polyaniline（PANi）and polypyrrole（PPy）are considered as the most promising electrode materials for supercapacitors owing to their simple synthesis,low cost and reversible oxidation/reduction process.In particular,one–dimensional nanostructured PANi possesses high specific area,large ratio of length to diameter and high electron transmission rate,thus it exhibits a great potential application as high–performance electrode materials.The energy storage property of one–dimensional nanostructured PANi depends greatly on its morphology and micro/nano-structure,which is greatly affected by the synthesis method.So far,several template–free methods for one–dimensional nanostructured PANi have been reported,such as interfacial polymerization,rapidly mixed polymerization and dilute polymerization and so on,but it exist some shortcomings,which limit its application to some extent,such as organic solvents are required for interfacial polymerization,while the low aniline concentration is need for rapidly mixed polymerization and dilute polymerization.Therefore,it is necessary to develop novel method for high–efficiently preparing one–dimensional nanostructured PANi in fully aqueous solution.In this work,three kinds of synthesis methods were presented to prepare PANi nanorods under flowing condition,and the nanostructure and capacitive property of as–prepared PANi nanorods and their composites with PPy were investigated.The main results were listed as following:（1）Preparation and capacitive properties of PANi nanorods prepared by coaxial flowing polymerization（CFP）in fully aqueous system.Aniline monomer and ammonium persulfate（APS）in hydrochloric acid solution were coaxial injected into PTFE microtube,and PANi nanorods were successfully prepared under flowing condition in fully aqueous system.It is found that the reaction solution did not be well mixed when aniline monomer was injected as outer layer and APS as inner layer.Thus in the further work aniline monomer was used as inner layer and APS was used as outer layer.The effects of the reaction tube diameter,relative flow rate of inner/outer layers,and molar ratio of monomer/oxidant on the morphology,structure and properties of PANi were further investigated.It is observed that with the increase of reaction tube diameter,relative flow rate of inner/outer layers,and molar ratio of monomer/oxidant,the band gap of PANi firstly decreased and then increased,whereas an oppositive trend could be found for the conductivity.Moreover,with the increase of diameter of reaction tube and relative flow rate of inner/outer layers,and decrease of molar ratio of monomer/oxidant,more PANi nanorods could be obtained.The polymerization parameters were optimized,that is to say,the reaction tube diameter is about 1.5 mm,relative flow rate is 10:10 and molar ratio is 1:2.The band gap,conductivity and yield of as–prepared PANi nanorods under the optimized condition were 2.35 eV,0.61 S cm–1 and20.6%,respectively.Moreover,PANi nanorods possessed the highest electrochemical properties among all the nanorods with the specific capacitance of 1008.0 F g–1 at the scan rate of 5 mV s–1and the specific capacitance retention of 65.4%after 500 cycles in 1.0 M H2SO4 electrolyte.（2）Preparation and capacitive properties of PANi nanorods prepared by coaxial flowing polymerization（CFP）in water–alcohol co–solvent system.Same coaxial polymerization condition was adapted except alcohols solvents were introduced to the inner layer.The influences of the nature of alcohols solvents（involving methanol,ethanol,ethylene glycol,isopropanol,glycerol and phenylcarbinol）,content of alcohols in water–alcohol co–solvent and aniline concentration on the morphology,structure and capacitive properties of PANi were investigated.The results showed that the polymerization rate became obviously slow by introducing alcohol solvent.It is found that the PANi nanorods with relatively small and narrow distribution of the diameter appeared in the presence of ethylene glycol,while relatively large size could be observed for phenylcarbinol,even irregular particles for glycerol.With the increase of content of ethylene glycol in inner layer,the conductivity of PANi nanorods increased gradually,whereas the band gap and yield decreased.Relative high aniline concentration was beneficial to the formation of PANi nanorods with large conductivity and high yield.However,serious aggregation of PANi nanorods could be occurred once the aniline concentration exceeded 0.06 M.Furthermore,PANi nanorods obtained in the presence of ethylene glycol had the largest conductivity of 0.76 S cm–1and the yield of 21.4%at the aniline concentration of 0.04 M.Moreover,the highest specific capacitance of 1162.6 F g–1 at scan rate of 5 mV s–1 and the specific capacitance retention of 67.9%after 500 cycles could be achieved in 1.0 M H2SO4 solution,being slightly better than those for than the PANi nanorods synthesized in fully aqueous solution.（3）Preparation and capacitive properties of PANi nanorods prepared by mixing flowing polymerization（MFP）.To improve the mixing degree of aniline monomers and APS,the reaction solutions were mixed under magnetic stirring before they were introduced the reactive microtube.It is found that the polymerization reaction rate can be effectively improved through pre–mixing.The influences of stirring rate,flow rate and pre–mixing temperature on the morphology and structure of PANi nanorods were investigated.It is found that that with the increase of the stirring rate and flow rate,the conductivity of PANi nanorods firstly increased and then decreased,while with the increase of stirring rate and decrease of flow rate,more nanorods could be obtained.Furthermore,relatively low pre–mixing temperature was helpful to improve chain orientation,conductivity and yield of PANi nanorods.Relatively large conductivity of 0.82 S cm–11 and yield of31.7%could be achieved for PANi nanorods prepared at the stirring rate of 1000 rpm,flow rate of10 ml h–11 and pre–mixing temperature of 25 oC.Moreover,as–prepared PANi nanorods exhibited the largest specific capacitance of 1137.1 F g–1 at scan rate of 5 mV s–1 and the specific capacitance retention of 68.6%after 500 cycles in 1.0 M H2SO4 solution,being better than the PANi nanorods obtained by CFP in fully aqueous system.（4）Preparation and capacitive properties of PANi nanorods prepared by thin–to–thick flowing polymerization（TFP）.To achieve a better balance between the number of seed and sequently growth of PANi chains,a thin–to–thick tube configuration was designed to prepare PANi nanorods,in which the seeds were produced in the relative thin reaction tube and the growth of PANi nanotube occurred in sequent thick tube.The effects of thin and thick tube length,flow rate and aniline concentration on the morphology and nanostructure of PANi nanorods were discussed.It is found that the polymerization reaction rate for TFP was faster than CFP but slower than MFP.The introducing of thin reaction tube can efficiently reduce the diameter of PANi nanorods.With the increase of thin and thick tube length as well as the decrease of flow rate,the conductivity of PANi nanorods was firstly increased and then reduced,whereas the yield gradually increased.Relatively large conductivity and high yield of PANi nanorods could be obtained at the high concentration of aniline monomers.The largest conductivity of 1.02 S cm–11 and yield of 27.4%could be achieved for the PANi nanorods prepared with thin tube length of 0.10 m,thick tube length of 2.0 m,flow rate of 10 ml h–11 and aniline concentration of 0.04 M.Moreover,as–prepared PANi nanorods exhibited the largest specific capacitance of 1440.0 F g–1 at scan rate of 5 mV s–1and the specific capacitance retention of 71.3%after 500 cycles,being the best performance among three kinds of the nanorods obtained by various flowing polymerization.（5）Preparation and capacitive properties of PANi nanorods and their PANi/PPy composites with core–shell structure.Three PANi nanorods prepared with above mentioned flowing methods under the optimized conditions were used as seeds,and their composites by covering PPy on the surface of PANi nanorods through in–situ polymerization.Electrochemical properties of PANi nanorods in neutral electrolyte were firstly investigated.It is found that compared with capacitive properties in acidic electrolyte,the specific capacitance and cyclic stability of PANi nanorods decrease obviously in neutral electrolyte.Furthermore,PANi nanorods prepared by TFP exhibited the highest specific capacitance of 312.0 F g–1 at the scan rate of 5 mV s–1 and the highest specific capacitance retention of 59.3%after 500 cycles in neutral electrolyte among three nanorods.Followingly,the influences of PANi nanorod as seed on the morphology and micro/nanostructure and properties of the PANi/PPy composites were discussed,and the feasibility for PANi/PPy composites as high–performance electrode materials in neutral electrolyte was evaluated.It is found that the composites by covering PPy on the surface of PANi nanorods as seeds exhibited the core–shell structure,and the diameter and conductivity of the composites increased obviously compared to PANi nanorods.Furthermore,the PANi/PPy composite by using PANi nanorods prepared through TFP as seeds showed the highest conductivity of 3.11 S cm–1.Great improvements on the specific capacitance and cyclic stability of the composites could be achieved,benefiting from strongπ–πinteraction between PANi core and PPy shell.The PANi/PPy composites by using PANi nanorods prepared through TFP as seeds exhibited the best capacitive properties with the specific capacitance of up to 1550.2 F g–1 at scan rate of 5 mV s–1,and the cyclic stability as high as 77.3%after 500 cycles.What is more,compared the PANi/PPy composites obtained by using PANi nanorods prepared via rapidly mixing polymerization as seeds and rGO/PANi–co–PPy,the PANi/PPy composites fabricated through flowing polymerization had higher energy storage properties,exhibiting greater potential as high–performance electrode material for supercapacitors in environmental friendly electrolytes. |
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